1. Technical Field
The present invention relates to a detection device particularly suitable for detection of a trace substance.
2. Related Art
In recent years, as one of sensitive spectroscopic techniques for detecting low-density sample molecules, surface enhanced Raman scattering (SERS) spectroscopy using surface plasmon resonance (SPR), in particular localized surface plasmon resonance (LSPR), has been attracting attention (Japanese Patent No. 3714671, JP-A-2000-356587). The SERS denotes a phenomenon that the Raman scattering light is enhanced 102 through 1014 times on a metal surface having a structure of providing unevenness in nanometer scale. The sample molecules are irradiated with an excitation light with a single wavelength such as a laser. The light with a scattering wavelength (the Raman scattering light) shifted from the wavelength of the excitation light as much as the molecular vibration energy of the sample molecules is spectroscopically detected to thereby obtain the fingerprint spectrum of the sample molecules. It becomes possible to identify the sample molecules based on the shape of the fingerprint spectrum.
The surface plasmon resonance sensor of this kind is formed by fixing metal fine particles made of, for example, gold or silver on a substrate. The detection device provided with this sensor irradiates the sample molecules adsorbed to the metal nanoparticles of the surface plasmon resonance sensor with light, and then detects the Raman scattering light thus enhanced.
Here, as one of the usages of the surface plasmon resonance sensor, there is cited, for example, monitoring of an environmental pollutant. In order to monitor the pollutant, it is required to detect the pollutant in real time.
However, according to the detection device described above, although it is possible to detect whether or not the sample molecules adsorbed to the metal nanoparticles of the surface plasmon resonance sensor are pollutants, the detection can be performed only once. Therefore, if the presence or absence of the sample molecules in space is detected a number of times in real time, it is not achievable to detect whether or not the sample molecules surely exist at a density equal to or higher than a certain level, or whether or not the density at which the sample molecules exist is surely equal to or lower than a certain level with improved reliability.